The use of thermocouple or heat-sensitive sensors in general as temperature sensors in such electrical systems is known.
However, although operational solutions exist for the electrical isolation of these thermocouple, electrically conductive sensors, the response time for this type of temperature sensor, i.e., the time resolution of thermocouple sensors, remains at around ten milliseconds, which restricts the use of thermocouples to thermal equilibrium conditions.
Heat radiation detectors, for example infrared radiation-sensitive cameras, offset this drawback, since they have faster response times and can measure temperature variations with a time resolution below 1 ms.
However, these heat radiation detectors require a field of view on the measured object with no concealed portions, which is not ordinarily possible on power modules. Indeed, the traditional encapsulation techniques do not generally make it possible to have unhindered visibility of the module, and this type of detector cannot be integrated into a component housing.
One solution making it possible to offset the drawbacks described above lies in the principle of using the power chip itself as the electronic temperature sensor, such that the temperature measurement can be done with calibrated series modules without damaging the encapsulation.
In principle, any electrical parameter depending on the temperature of a power chip, i.e., a controlled electronic switch such as an IGBT (Inverse Gate Bipolar Transistor), can be used for electronic measurement of the junction temperature.
The use of the evolution as a function of the temperature of the voltage drop of the semiconductor junction in direct conduction, measured between the two main power electrodes (anode-cathode or drain-source or collector-emitter) of the electronic switch, for example a silicon junction (in case of a bipolar component) or an ohmic region (case of a field effect component), is of the utmost interest, since it takes advantage of a temperature response that is most often substantially linear over a wide temperature band.
For the bipolar components, the exploitation of the evolution as a function of the temperature, denoted T, of the diffusion voltage VCE(T) with a low current is known to determine the temperature of a semiconductor junction without needing an additional direct temperature sensor. It is for example described in the article by Scheuermann et al., entitled “Investigations on the VCE(T)—Method to determine the junction temperature by using the chip itself as sensor” published in Proceedings PCIM Europe 2009 Conference, pages 802 to 807.
For example, the slope of the temperature characteristic of the diffusion voltage is approximately −2 mV/K for an injection measurement current of 200 mA injected into the current IGBT chips.
In order to have good precision of the junction temperature, it is necessary to find the right compromise regarding the choice of the measurement current, which must not cause an ohmic voltage drop and auto-heating of the chip, which must be sufficient to preserve good immunity to parasites.
One of the difficulties of this indirect electronic temperature measurement technique lies in the precise and quick measurement of a small voltage drop across the terminals of a controlled electronic switch, for example across the terminals of an IGBT, working in nominal service in a switching cell with a high voltage, for example several tens or hundreds of volts, with switched currents of at least several amperes, or even several hundreds of amperes.
A first embodiment of an electronic temperature sensor implementing the VCE(T) technique is described in the article by Amgad RASHED et al., entitled “Automatic characterization of IGBT modules placed in an aging process by heat cycling” and presented to the Congrès d'électronique de puissance du future conference, Bordeaux 2012.
The electronic temperature sensor described in this article, and associated itself with an IGBT switch of a switching cell of a two-phase inverter, includes a VCE measuring circuit connected across the power terminals of the IGBT transistor and an injection current source for a measuring current of 100 mA, made in the form of a simple ballast resistance, therefore depending on the supply voltage.
The VCE measuring circuit is made up of a voltage clipper to limit the voltage experienced by the measuring circuit when the tested transistor is blocked, and a voltage-current converter.
A second embodiment of an electronic temperature sensor implementing the VCE(T) technique is disclosed in the article by D. Bergogne et al. entitled “An estimation method of the channel temperature of power MOS devices” published in Power Electronics Specialists Conference, 2000, PESC 00, 2000 IEEE 31st, vol. 3, pp. 1594-1599.
The technical problem is to simplify the structure of the electronic temperature sensor, in particular the VCE measurement circuit, in terms of lack of high-voltage active components, and to make the structure independent of the supply voltage level.
One related technical problem is to improve the reliability of the electronic temperature sensor.